In a semiconductor device, wire bonding is used to connect a pad of the semiconductor device to an external connection terminal through a metal wire to exchange electrical signals with the outside. Since the wire bonding is a mechanical process of bonding a wire formed of gold or the like to the pad of the semiconductor device with use of heat, ultrasound, or weight, the semiconductor device may thereby receive damage. Detail is described with reference to FIGS. 11(a) and 11(b). As illustrated, the ball bonder comprises a capillary C through which a bonding wire 14 is fed. The capillary has a tip having a beveled corner 13. A wire ball 15 formed at a tip of the bonding wire 14 is press-fitted, by downward movement of the capillary C, to a topmost layer metal film 3 in a pad opening formed in the semiconductor device, becoming a crushed ball 16, and the bonding wire 14 is thus bonded to the topmost layer metal film 3 in the pad opening. During crushing of the wire ball 15 into the crushed ball 16, the beveled corner 13 deforms the wire ball as illustrated in FIG. 11(b). At this time, a crack 18 may develop in an insulating film 5 formed under the pad opening, which affects reliability of the semiconductor device.
Patent Literature 1 describes that, by devising a capillary structure of a ball bonding apparatus for the purpose of preventing a crack, bonding damage is inhibited, and development of a crack can be inhibited.
In Background Art of Patent Literature 2, it is described that, in order to keep strength against bonding so as to prevent a crack, there is formed a thick metal film in the pad opening in direct contact with the bonding wire. The metal film itself absorbs the bonding damage, inhibiting a crack and enhancing the crack resistance of the pad structure itself.
Further, in Patent Literature 3, as illustrated in FIG. 12, there is disclosed a pad structure in which an effective thickness of an insulating film formed under a pad opening 9 that receives the bonding damage is increased. A second metal film 2 is not formed under the topmost layer metal film 3 in the pad opening 9. A thickness of insulating films between a first metal film 1 and the topmost layer metal film 3 is a sum of a thickness of a second insulating film 4 and a thickness of a third insulating film 5, and an effective thickness of the insulating films formed under the pad opening 9 that receives the bonding damage is increased. The thick insulating film absorbs the bonding damage, inhibiting a crack. Arrangement of wiring and the like of the first metal film 1 under the pad opening 9 can reduce the chip size.